The invention relates to an apparatus for monitoring appliances and machines with rotating components, particularly for monitoring compressors, vacuum pumps and other pumps, having a sensor, an evaluation electronics unit and an interface for the output of signals.
In appliances and machines with rotating components, particularly also in compressors, vacuum pumps and other pumps, it is at least expedient—in many other cases even prescribed and absolutely necessary—to continually check whether the appliance or the machine is still operating perfectly. In many cases, it is undesirable and infeasible to wait until the machine or the appliance breaks down. This is particularly true in the case of pumps, e.g. in industrial installations, where not only may entire installation parts break down when a pump fails but where relatively great damage may also arise on account of the failure. There is therefore a great deal of concern that abnormalities in operating behavior be detected before the pump fails so that the necessary measures can be initiated (switching off an installation part, rerouting currents, etc.). Examples of faults which one would wish to detect are bearing wear, imbalance, disorientation, pipeline distortion, cavitation phenomena, etc.
The prior art for vibration monitoring firstly covers intermittent measurements using a handheld measuring instrument (cf. DE 199 17 541 A1, for example). The measurements using a handheld measuring instrument have the drawback that no continuous monitoring is performed, which means that temporary inadmissible operating states which would result in premature damage to the pump are not recognized. Reliable state monitoring is therefore not possible. Damage which appears outside the measurement cycle is not recognized either. In addition, expert knowledge is required in order to evaluate the measured data. For measurements in the chemical industry, where there are areas with an explosion risk, the handheld measuring instruments need to be protected against explosion.
Further measuring systems for vibration monitoring based on the prior art use one or more vibration sensors. These sensors continuously capture information about the vibration behavior and are combined in an external evaluation unit. The evaluation unit performs the signal analysis. The evaluation unit monitors threshold values and/or provides extensive trend information from frequency analysis. The communication for process control is carried out by switching contacts, serial interfaces or using field bus systems. The drawback of such systems is that they are expensive to purchase and complex to install, since sensors and evaluation electronics are installed at separate locations. The interface link to the process control is also complex. In addition, extensive expert knowledge is required in order to configure such systems and in order to evaluate the measured data. For areas with a risk of explosion, it is not only necessary to use vibration sensors which are protected against explosion; rather, the connection to the evaluation appliances must also be made using appropriate explosion protection barriers. This makes such systems complex and expensive.
DE 102 28 389 B4 discloses a vibration sensor of the type cited at the outset for monitoring the state of rotating components or bearings with an integrated signal conditioning unit. For the purpose of communication for process control, there are two switching outputs available, one switching output tripping a preliminary alarm and the other switching output tripping a main alarm. For monitoring vibrations in bearings, the system is configured at bearing frequencies, and in the case of rotating components at freely selectable frequency amplitudes. The level adjustment is performed using calibration in normal operation. The drawback of this system is that the communication for process control is effected only using two switching contacts. Continuous trend data therefore cannot be transmitted. In addition, expert knowledge is necessary in order to configure such a system.
In particular, however, there is the drawback that frequency analysis requires many measurement points which are recorded at a high sampling frequency. For an accuracy of 0.5 Hz in the frequency spectrum, which is at least necessary for low frequencies, and a frequency range up to 10 kHz, the time signal needs to be sampled at least twice the frequency of the maximum frequency of the spectrum (Nyquist theorem). The sampling frequency therefore needs to be 20,000 values per second. The storage depth, which is equal to the sampling frequency divided by the frequency resolution, then needs to be 40,000 values per measurement. The processing (Fourier transformation) of this large volume of data requires a high computer power and a corresponding large main memory. The high computer power which is required necessitates a high power consumption, however. The large currents again mean that particularly complex measures need to be taken for explosion protection in environments with a risk of explosion. If the total power consumption is no more than 20 mA, it is possible to implement the intrinsically safe circuit. This can then be operated without special measures in the environment with a risk of explosion. On the basis of the prior art, these currents are not sufficient to operate microprocessors which need to process the aforementioned volume of data.
An object is to provide an apparatus of the type cited at the outset which allows the rotating components to be monitored using little computation power and hence low power consumption. In addition, the interface is intended to be able to be used to output different data about the operating state.